[lldb] Fix crash missing MSInheritanceAttr with DWARF on Windows (llvm#112928)

Member pointers refer to data or function members of a `CXXRecordDecl` and
require a `MSInheritanceAttr` in order to be complete. Without that we
cannot calculate their size in memory. The attempt has been causing a crash
further down in the clang AST context. In order to implement the feature,
DWARF will need a new attribtue to convey the information. For the moment,
this patch teaches LLDB to handle to situation and avoid the crash.

Author: weliveindetail

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

@@ -2771,6 +2771,9 @@ static bool GetCompleteQualType(clang::ASTContext *ast,
         ast, llvm::cast<clang::AttributedType>(qual_type)->getModifiedType(),
         allow_completion);
 
+  case clang::Type::MemberPointer:
+    return !qual_type.getTypePtr()->isIncompleteType();
+
   default:
     break;
   }

lldb/test/Shell/SymbolFile/DWARF/x86/member-pointers.cpp

@@ -0,0 +1,24 @@
+// REQUIRES: lld
+
+// Itanium ABI:
+// RUN: %clang --target=x86_64-pc-linux -gdwarf -c -o %t_linux.o %s
+// RUN: %lldb -f %t_linux.o -b -o "target variable mp" | FileCheck %s
+//
+// CHECK: (char SI::*) mp = 0x0000000000000000
+
+// Microsoft ABI:
+// RUN: %clang_cl --target=x86_64-windows-msvc -c -gdwarf %s -o %t_win.obj
+// RUN: lld-link /out:%t_win.exe %t_win.obj /nodefaultlib /entry:main /debug
+// RUN: %lldb -f %t_win.exe -b -o "target variable mp" | FileCheck --check-prefix=CHECK-MSVC %s
+//
+// DWARF has no representation of MSInheritanceAttr, so we cannot determine the size
+// of member-pointers yet. For the moment, make sure we don't crash on such variables.
+// CHECK-MSVC: error: Unable to determine byte size.
+
+struct SI {
+  char si;
+};
+
+char SI::*mp = &SI::si;
+
+int main() { return 0; }